Coconut

Morphology

Introduction

The coconut belongs to the family of palms Palmae included under the lower group of flowering plants known as the monocotyledons.
It occupies a conspicuous position in the vegetable kingdom owing to certain features characteristic of the palms, viz., comparatively slow growth; an unusual thickening at the base of the trunk giving mechanical rigidity; generally unbranched, erect, cylindrical, pillar-like stem covered with heavy scars of old leaf bases; a compact magnificent crown of gigantic, feathery, glossy, thick-cuticled leaves sheathed at the base providing firm attachment to the stem, oriented at the top of the trunk rendering a natural beauty and elegance; a branched inflorescence enclosed in a sheath collectively known as the spadix; the absence of tap root and the continually growing terminal bud commonly known as the 'cabbage'.

Brief botanical description Family : Palmae Name; Cocos nucifera L.

It is a tall, stately, unarmed palm growing to a height of 12 to 24 m.
The trunk is stout, flexuous, annulate, rarely stands vertically, but makes a gradual curve, rising form a swollen base surrounded by a mass of adventitious roots.
The stem is marked by rings of leaf-scars which are often not prominent at the base.
Leaves are large, long, pinnatisect, borne on the crown; leaflets equidistant, 60 cm to 90 cm long, narrow, tapering, linear, lanceolate, coriaceous, flaccid; petioles stout, 90 cm to 150 cm long.

The Stem

When the bole reaches the full stage of its development, the stem becomes visible.
The thickness of the stem generally depends upon the vigour of the tree, hereditary variation and soil conditions.
In the initial years of the growth of the tree the stem gradually increases in thickness and this thickness is maintained throughout.
Growth of the stem may however, become thinner as the tree gets older and meets with unfavourable conditions.

The unevenness thus produced, though slight, persists and this is a visual record of the vicissitudes through which the palm has passed.
The stem of the coconut grows erect under normal conditions.
But trees on the margins of the plantations often lean away towards light.
In places where winds often prevail, the trees will lean along the directions of the wind.
Any injury caused to the stem remains as such because the tissues of the stem have no capacity to repair the injury due to the absence of meristematic activity.
It can however withstand considerable amount of damage due to the presence of fibrous tissue in the trunk.
These strands are generally much closer together towards the middle of the tree enabling it to withstand considerable lateral strain particularly in times of severe winds and gales.
The coconut tree has only one growing point, the bud. If this bud is killed, the tree dies.
The bud produces a succession of leaves.
When the leaves grow old they are shed, leaving a rough pitted scar on the trunk which encircles the whole stem.
From the counts of these scars the age of the trees can be approximately determined, as roughly 12 to 14 such successive scars left on the tree correspond to a year of growth of the tree.
It is also possible to gauge the vigour of the tree from these scars.
In a bearing tree the scars left by the inflorescence stalk may be seen on the stem in the middle above the widest portion of the leaf scar.
The interspace between successive leaf scars may serve as an index of the bearing capacity of the tree or the environment under which it is grown.

The Leaf

Every tree has a crown of leaves oriented at the top of the trunk consisting of opened leaves and those in the bud in various stages of development.
The number of leaves in the crown varies depending on the conditions prevailing, viz., method of cultivation, nutritional status of the soil, sunlight, etc.
In adult trees, the crown comprises about 30 to 40 opened leaves.
There are generally four sets of leaves in the crown.
The first set consists of ten to twelve leaves counted from the oldest leaf, from the axils of which the bunches have already been harvested.

The majority of these are of very little value to the tree having past their prime.
The next set consisting of ten to fourteen leaves will be those supporting fruit bunches in the different stages of development.
The third set includes ten to twelve opened leaves in the axils of which are found spadices in various stages of development.
The soft and brittle bud in the centre of the crown is the most rapidly growing part of the tree.
The bud is rich in phosphates and potash and has a 'nutty' flavour.
It is considered a great delicacy.
The number of leaves inside the 'cabbage' has to be generally ranging from the same number to one and a half times the number of leaves opened outside.
The bud is protected by stipules, which form a sort of fibrous bandage binding the tender leaves.
This fibrous sheath persists for some time till the leaves mature and become strong enough to withstand severe winds.
The bud produces leaves in succession.
the young leaf first appears in the centre of the crown as a pointed arrow and in this stage all the leaflets are held together.
The top leaflets open out as the leaf grows and it takes four to five months to completely emerge out of the sheath.
The leaf is considered to be fully open when the lowermost of the leaflets has emerged.
When the tip of the leaf appears in the centre of the crown it is in line with the stem, i.e., almost perpendicular to the ground.
It is then gradually pushed to one side to provide space for the younger set of leaves.
As the leaf gets older, it bends down and by the time it dries up and is about to shed, i.e., within about two and a half to three years from the emergence of the leaf.
The tip which once faced the sky now points downwards to the ground.
The leaves are so arranged on the crown that each leaf gets the maximum amount of light.
This is secured by an arrangement of leaves on the crown in five spirals which run in clock-wise or anti-clockwise direction giving rise to right or left spirals respectively.
The phyllotaxy of each spiral is nearly two-fifths. Starting from the first leaf and making nearly two complete rounds of the stem the sixth leaf is reached.
If the bunches hang towards the right of the petiole, the spiral is towards the left and when the bunches hang towards the left of the petiole, the spiral is towards the right.
Even though the direction of the spiral varies in different trees, it remains the same throughout the life of any particular tree.
The leaf consists of a rachis popularly known as leaf-stalk (or petiole) and the leaflets.
The leaf-stalk continues as a mid-rib or rachis till the tip of the leaf where it merges into the green leaflets.
The upper half of the leaf can withstand strains from above as well as from the sides
The leaf stalk attaches the leaf to the stem by means of a sheath in the form of a bracket firmly clasping the stem with its wings neatly round it, providing mechanical strength for it to withstand considerable strain from the wind and the weight of the bunch.
The centre of attachment is, however, not so strong, for if the joint at the wings is cut, it is quite easy to tear away the leaf from the stem which is still quite tender where it is protected by the thick butt of the leaf bracket.
When young, the stipules from a part of the leaf stalk and surround the whole stem.
In young trees these stipules frequently persist unbroken till the leaf dies.
The shape of the leaf stalk is of importance and there is a certain natural variation in this.
The upper surface is nearly flat or just sufficiently grooved to prevent water from running to its side.
The groove down the centre of the mid-rib is of interest as this canalises sufficient water which is allowed to run down into the crown and from there down the stem to the base of the bole.
The lower surface is a round keel which thickens out considerably at the base thus forming a supporting bracket.
This rounded keel should be deep, as a shallow keeled leaf stalk is unable to support the weight of the green bunch.
At the same time the leaf stalk should be wide so as to lessen the chances of the bunch from slipping off the support.
The leaf stalk should also be short, as a short leaf stalk denotes a short bunch.
If the stalk of the bunch is short, the bunch will be nearer to the stem and this brings about less strain on the leaf bracket.
The number of leaflets on a leaf varies from 200 to 250. Where the number is small the leaflets are usually narrow and are farther apart, which is an undesirable character.
The leaflets near the base of the leaf as well as those near the apex are much shorter and narrower than those situated in the middle.
The longest leaflets are in the lower one-third of the leaflet-bearing region.
It is thus clear that there is great variation in the area of the leaf surface in different trees.
The attachment of leaflets at different part of the leaf varies greatly, but in all cases it is so arranged that it throws water off the mid-rib down the leaflets so that it drips down at the ends.
In the case of young leaves, these are more or less vertical and in this case any water falling on them runs down into the crown.
The leaflet consists of a central strong mid-rib with a blade on each side.
The blade is tough and leathery with green shining upper surface.
The leaflets partially close longitudinally in the shade, cloudy weather or at night, while in full sunlight they remain open

The Root

The coconut palm has an adventitious root system as typical of a monocot, i.e., it produces numerous uniformly thick roots from the base of the stem almost throughout its life.
The roots radiate from all the sides and are generally disposed to keep the direction in which they start.
These are the main roots.

The total number of such roots in a tree depends upon its age and the environment.
On the poor sandy soils of the Malabar Coast (India), they may vary from 1,500 to 2,500 in a tree aged about 25 years and 3,620 roots in a 60 to 70 years-old tree.
The number of roots counted on a bole usually varies from 4,000 to 7,000.
Although numbers much higher than these are rare, it is interesting to note that as many as 11,360 roots have been counted on a bole of a very old tree at the Central Coconut Research Station, Kayangulam (loose sandy soil).
The main roots measure 6 m in length on an average and in rare instances they may grow even up to 25 m. they are usually of uniform thickness of about 8 mm in diameter.
Under certain environments (when mechanically or otherwise injured) they produce one or more branches which are almost as thick as the original roots.
The main roots and the branch-roots are generally long-lived, while the rootlets, particularly the terriotories and their branches are short-lived.
However, the latter are replaced often during favorable conditions.
Coconut roots are also provided with numerous lenticel-like outgrowths or ventilators which may be called 'breathing organs', 'breathing roots' or 'pneumatophores', which help in the exchange of gases.
These white, pointed breathing roots are seen mostly on the main roots and sparsely on the rootlets.
Normally, roots are not formed very much above the bole region even when buried in the ground.
But, when the tree is old or when raised on water-logged areas, the roots commence to die from the apex upwards.
When this stage is reached, the tree, in order to maintain itself, commences to form new roots above the normal root-producing zone at the base of the stem.
These are termed aerial roots.

The Inflorescence

Inflorescence of the coconut are formed in the axils of every leaf of a bearing tree.
Early workers on coconut believed that inflorescences were formed in the axils of very third leaf.

It is true that some axils fail to throw out inflorescence because the latter become abortive.
But the production of such inflorescence has not been observed to have any definite relation with others.
The coconut is a monoecious plant producing male and female flowers separately on the same tree.
There are also palms which produce either completely male or female flowers.
The tendency to produce completely male inflorescences is frequently observed when the palm produces the spadix for the first time in its life.
Sometimes, this tendency is also manifested by trees which are given rest after a prolonged period of tapping for toddy.
There is also considerable variation in the frequency of bearing such inflorescences.
Some trees will produce their second or third inflorescence with female flowers in addition to male flowers, while others will not bear female flowers even in the sixth inflorescence.
The coconut produces inflorescences in continuous succession.
If one succeeds the other rapidly, or if the flowering period of each is sufficiently prolonged, it happens that before an inflorescence completes its flowering phase, the next one might be in flowering, brining in chances of overlapping and consequent inter-spadix pollination.
This frequently happens in dwarf palms and sometimes during the months of May, September and October in tall palms.
The inflorescence appears at first in the axil of a leaf as a pear shaped flat structure.
At this time, it is completely protected by two sheaths and is collectively known as the spadix.
The outer sheath is thick and fibrous while the inner one is more yellow and often fibrous and somewhat flat in nature.
In course of time, when the spadix is full grown, it becomes more cylindrical especially in the upper half and the distension of the inflorescence within causes great pressure on the walls of the spathe.
The inflorescence consists of many flower bearing ramifications or spikelets situated on a central axis or a peduncle.
Its size varies from 0.75 m to 2 m in length depending upon the individual palm.
When the inflorescence is enclosed within the spathe, the branches lie close to the main axis and the whole is so tightly packed that it is quite impossible for any of the individual flowers to open before the spathe splits.
Sometimes, a few flowers open as soon as the spathe splits.
At other times, none of the flowers open until the branches of the inflorescence have spread out.
Each branch is fringed and crowded with numerous male flowers from the tip downwards and bears lower down one or more female flowers, all the flowers being sessile or sub-sessile.

The Male Flower

The male flowers exceed the female ones in the same sapdix and may vary from a few hundreds to thousands depending on the number of ramifications in the spadix and the length of the flower bearing region.
They are the first to open.
Each male flower has six yellow perianth or floral leaves arranged in two whorls, the inner three alternating with the outer.
The inner perianth parts are more than three times the size of the outer ones.
Enclosed in this floral envelope, three are six hammer shaped stamens, which yield large quantities of powdery yellow pollen.
In the centre of each flower, there is a rudimentary or abortive pistil which divides at its apex into three teeth, each bearing a nectar gland, the nectar of which attracts ants, bees and other insects.
The flowers on the upper spikes of the inflorescence and those situated on the sides of the female flowers are the first to open and commence opening from he apex of the spike and extends downwards.
Sometimes few flowers may open out of order. The flowers bloom throughout the day, most of them blooming from 8 A.M. to 10 A.M.

The Female Flower

Unlike the male flowers, the female flowers are comparatively few in number in an inflorescence.
They may vary from 0 to 300 in each spadix depending on conditions prevailing, viz., nature of the tree, cultivation, manuring, season of the year, age of bearing, etc.
At the time of opening of the spathe, the female flower is a small spherical body, about 1.3 cm in diameter with great resemblance to a small nut and is popularly known as a button
The female flowers, like males, consist of six floral leaves which are thicker, intricately arranged and tightly folded over the inner parts of the flower completely enveloping the pistil.
From the tip of the pistil, there extend downwards three ridges which make the whole ovary look globosely three-sided, each side being provided at its tip with a groove.
These three grooves meet in the centre of the apex and form the stigma.
After the inflorescence opens, and before fertilization takes place, the mass of fibrous tissue continues to increase in size and ultimately forces apart the floral leaves disclosing only its rounded upper surface which is surmounted by a white nipple.
This nipple is marked by three equidistant grooves which meet at its apex and thus divide it into three triangular sections.
When the female flower is ripe, these three segments separate and stand erect as three teeth, exposing the stigmatic surface on which the pollen is to fall in order that the flower may be fertilized.
These three teeth constitute the stigma.
Normally it is impossible for fertilization to occur before the stigma is ripe and this does not happen until long after the opening of the inflorescence.
When the fertilization is complete, the stigma ultimately turns brown and the tissues around it collapse, forming a small black, more or less circular area containing three shrivelled teeth at the apex of the young fruit.
The six floral leaves increase slightly in size, and form the whorl of perianth leaves which persist at the base of the fruit till it matures and dries.

The number of female flowers

The number of female flowers in the inflorescence is variable. There is a difference in the production of female flowers among the trees as well as among the inflorescence of the same tree,
The variation among the trees of the same age and receiving the same treatment is genetical.
The average number of female flowers per tree in the group "good" is about 151, for the group "medium" about 120 and for the group "poor" only 41.

Seasonal variation in the production of female flowers

There is much variation in the number of female flowers produced during the different months.
This difference is partly due to the differences in the number of spadices opened in the different months.
But when the average number of female flowers per spadix are compared, similar differences are also noticeable.
It is generally high during the months of March to May, the highest being in May.

The Pollen

When the anthers are fully mature, the pollen sacs burst along two longitudinal slits which coincide with the partitions of the pollen sacs and shed their pollen before the opening of the male flower.
The pollen grains are spherical and smooth when very fresh.
On exposure for a few seconds, they turn ellipsoidal with a longitudinal groove in the middle and they measure about 0.063 mm in length and 0.020 mm in breadth at the centre.
In the mature pollen grain, there are three nuclei one of which is larger than the remaining two.

The Fruit

In the young fruit, particularly until the fruit is well developed, it varies in colour depending on the general colour of the parent tree.
The fruit of the coconut, botanically known as a fibrous drupe and popularly the 'nut', consists internally of the endopsermous kernel with the embryo embedded in it and externally protected by the fruit coat known as the pericarp which consits of three distinct and well defined regions, viz., the exocarp or epicarp, the mesocarp and the endocarp.

The outermost region of the fruit coat is the exocarp (or epicarp) which consists of a tough smooth and hard fibrous skin where as in the ripe fruit it assumes green, red, yellow or brown colour.
It may assume various shades, viz., bright red, pale yellow, pale green, red brown, brown green or dark green.
Immediately below this is the fleshy portion known as the mesocarp which in the young fruit is astringent and in rare instances sweet and edible.
When the nut develops and mature, this region turns fibrous.
The thickness of this region is variable ranging from 2 cm to 15 cm.
Below the fibrous covering is the endocarp which when the fruit matures, develops into the sell.
This hard shell in the cross-section of the fruit is more or less triangular in shape and has three ridges on the outside which alternate with the ridges on he fruit.
At the basal end of the fruit where it is attached to the fruit stalk, there three eyes, one on each carpel, normally two of which are quite hard and the third one soft.
One side of he triangular cross-section or the carpel of the fruit is narrower than the other two sides.
On an examination of the nut, it is found that one of three segments has a wider angel than the other two.
It is in this widest segment that the soft or germinating eye is situated which is easily recognised on the nut as it is a bigger than the other two.
The fibre over this eye is also softer and generally was compact than elsewhere.
The seed or the kernel or meat of the fruit is well protected by the hard shell and lies immediately below it.
Placed between the meat and the shell, is the seed coat which is firmly attached to the meat.
The meat in the ordinary nut is about 13mm thick, but occasionally the thickness may go up to 20mm.
In dwarf and ornamental varieties on the other hand, the kernel is generally very much thinner.
At the apex of the nut, immediately below the soft eye and embedded in the kernel lies a peg-like body, the germ or embryo, which, on germination, commences to grow and forces its way through the soft eye.
Within the kernel is a cavity which in the unripe fruit is completely filled with the liquid popularly known as 'coconut water'.
As the fruit ripens, this water gets very much reduced filling the cavity only partially.

The Development Of The Fruit

aa After fertilisation, the growth of the fruit follows with pericarp developing most rapidly at the basal region which remains soft and whitish until the fruit is nearly mature.
The endocarp is already differentiated as a soft, creamy, white structure long before the time of fertilisation.
As the fruit develops and matures, the embryo-sac increases in size, leaving a large vacuole at the centre.
The embryo-sac is at first rounded and then it elongates and widens until near maturity.
The fruit loses its conical shape in the early part of the elongating period and becomes spheroidal to orbicular a it matures.
When the fruit is young, the mesocarp comprises the major portion of the pericarp, being wider near the stigmas and sides and very narrow at the portion which attaches the fruit to the rachilla.
During its development, the mesocarp up to maturity increases in thickness in the region opposite the stigmas or near the micropylar end of the ovules.
The exocarp always remains tough and hard and loses its green colour when old, the final colour varying with the variety.
The pericarp undergoes differentiation long before the ovules are formed, into
an outer single layer of squarish to elongated cells comprising the exocarp.
the large isodiametric cells of he mesocarp; and c)the small isodiametric cells of the endocarp
There are three eyes, and when only one embryo is developed one eye become functional and the other two are non-functional.
The fertile eye appearing to be a depression which is due to the failure of the endocarp to lignify.
The remainder of the covering of the eye, is composed of spongy parenchymatous tissue which morphologically belongs to the endocarp and the fertile eye which became covered only by a very thin plate of lignified cells formed from the palisaded layer of the endocarp and from the outer integument of the fertile ovule.

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Tamilnadu

Coconut

About Coconut

History

Morphology and Growth

Coconut Management

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